JPS5952981A - Digital subtraction system for X-ray TV equipment - Google Patents

Abstract

PURPOSE:To obtain an output emphasizing a contrast suitably with an X-ray TV device having the function of digital subtraction, by using the maximum and minimum value of the density of each picture element of a subtraction image obtained during the first one frame period as a basis. CONSTITUTION:An image before a contrast medium is injected is stored in a frame memory 11 as a mask image and that after the contrast medium is injected is stored in another frame memory 12 as a live image. The density data of every picture element between the memories 11 and 12 are subtracted at a real time by a subtracting circuit 13 and the difference is outputted to a monitor TV16 after its contrast is emphasized by passing through an enhancement circuit 14 and converted into an analog value by means of a D/A converter 15. Comparators 18a and 18b compare at every picture element the maximum and minimum values held by registers 19a and 19b as the density data of the picture elements, respectively. Thus the data of the maximum value and minimum value are selected among the entire picture element and inputted into the enhancement circuit 14, and the circuit 14 assigns the maximum and minimum vaues to a suitability regarding the density and gives the highest suitability to the picture element of an intermediate value.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital subtraction system in which contrast enhancement of a differential image is performed in an X-ray TV apparatus having a digital subtraction function.

The digital subtraction system calculates the difference between two images before and after contrast agent injection, and displays only the image of the blood vessel containing the contrast agent in real time. However, the contrast agent concentration is generally low, so the contrast is emphasized. and output the image. Conventionally, a method has been adopted in which a difference value for white and black levels is set in advance on an operation panel. However, it was difficult to obtain an appropriate degree of emphasis each time.

SUMMARY OF THE INVENTION An object of the present invention is to provide a digital subtraction system for an X-ray TV apparatus that can automatically adjust the degree of contrast enhancement to an appropriate state for each image with respect to difference images output in real time.

In order to achieve this objective, the idea of the present invention lies in the following points. In the serial mode using pulsed X-ray radiation, subtraction is performed approximately once or twice per second, so the same output image is repeatedly output for 30 or 15 frame periods.

Therefore, during the first frame period, the maximum and minimum density values of each pixel of the subtraction image are detected, and based on this, the enhancement non-1lliJ path is used to calculate the values during subsequent frame periods. Automatically set contrast enhancement level. If this is done continuously, an image with optimum contrast enhancement will be output and displayed for each image, except during the first frame period when the output image changes.

Next, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic IJ block diagram thereof. ,,10
11 is a frame memory for mask images, 12 is a frame memory for live images, and 13 is a subtraction circuit.

Frame memory 11 uses the image before contrast agent injection as a mask image
The data is stored permanently. After the contrast agent is injected, the data stream is switched and stored in the frame memory 12 as a live image.

The subtraction circuit 13 subtracts data at each pixel of the mask image frame memory 11 from the live image frame memory 12, and outputs a difference image. Also, 14 is an enhancement circuit, 15 is a D/A converter, and 16 is a monitor T.
V, 17 is a VDR or VTRf. Furthermore, 20 is a detector, which includes comparators 18a and 1.8b, a maximum value hold register 19a, and a minimum value hold register 19.
It consists of b.

As mentioned above, the density data for each pixel between the two frame memories 11 and 12 is subtracted in real time by the subtraction circuit 13, and the difference is contrast-enhanced through the enhancement circuit 14, and then VA conversion is performed. The analog value is converted into an analog value by the device 15 and output to the monitor TV 16. Second
The figure is an output diagram of the subtraction circuit 13, and FIG.
3 is an output diagram of the converter 15. FIG.

Comparator 1.8a compares the density data for each pixel with the maximum value data in register 1.9a, and comparator 18b similarly compares the minimum value data in register 19b. , the maximum value and the minimum value data are selected over all pixels and inputted to the enforcement circuit 14. Therefore, assign the maximum value and the minimum value to the optimal degree with respect to a degree,
For pixels having other intermediate values as well, the optimal degree of density proportionally proportional to the assigned optimal degree is given. The resulting output diagram is shown in FIG. Note that if the screen area where each data of the maximum value and minimum value of a degree exists is known in advance, it is not necessary to process all pixels.

In the present invention, paying attention to the fact that the difference images output during a plurality of frame periods are in the same state, especially in the case of serial mode, a circuit 20 is added to detect the maximum density value and minimum density value in a pixel. The maximum and minimum densities are detected during the first frame period, and from the next frame an image with optimal contrast enhancement is automatically obtained, and this is true for all periods. Even if the difference image changes with each X-ray exposure, an appropriate contrast image is always obtained for all but the first frame.

Note that the present invention can also be applied to a continuously changing coherent mode in which differential images between multiple frames are not the same, since the images before and after the change do not change drastically and appear to be approximately the same. . In this case, the degree of enhancement is always determined by the maximum and minimum values of the image one frame before, but as mentioned above, in X-ray contrast images, the image condition can be handled without changing sharply. As shown in the figure, the concentration of contrast medium in blood vessels and the X-ray absorption of the subject differ depending on the subject or region, so it is practically difficult to determine the degree of enhancement in advance, but the present invention Interpret problems and enable observation of subtraction images with optimal contrast in real time.

Another effect of the present invention is that analog recording (VDR, VTR,
etc.), the input signal becomes smaller and becomes more susceptible to the noise of the recording medium, resulting in a secondary problem of deterioration of image quality, but this will also be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIGS. 2 to 4 are diagrams for explaining the operation of the present invention. The figure is an output diagram of the enhancement circuit, and FIG. 4 II-j is an output diagram of the D/A converter. 13 is a subtraction circuit, 14 is an enforcement circuit, 18
is a comparator, 19 is a register, and 20 is a detector. Figure 2

Claims (1)

[Claims] A subtraction image processing device comprising an image pickup tube, a mask image memory, a live image memory, a subtracter of the former two, an enhancement circuit, a digital converter, a monitor TV, and a VDR or VTR, A detection circuit is added to detect the maximum and minimum values of the density over all pixels or any area of the difference image obtained from the subtracter, and the enhancement circuit calculates the density of each pixel using these two values. A digital subtraction system for an X-ray TV device, which outputs optimally converted data and performs contrast enhancement.